Iron-based composition for fuel element

ABSTRACT

Disclosed embodiments include fuel assemblies, fuel element, cladding material, methods of making a fuel element, and methods of using same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.15/076,475, filed Mar. 21, 2016. U.S. application Ser. No. 15/076,475 isa continuation of U.S. application Ser. No. 13/794,589, filed Mar. 11,2013, now U.S. Pat. No. 9,303,295, which application claims the benefitof U.S. Provisional Application No. 61/747,054, filed Dec. 28, 2012,which applications are incorporated herein by reference in theirentirety.

BACKGROUND

The present patent application relates to a fuel element including acladding material and methods related to same.

SUMMARY

Disclosed embodiments include fuel elements, fuel assemblies, claddingmaterials, and methods of making and using same.

The foregoing is a summary and thus may contain simplifications,generalizations, inclusions, and/or omissions of detail; consequently,those skilled in the art will appreciate that the summary isillustrative only and is NOT intended to be in any way limiting. Inaddition to any illustrative aspects, embodiments, and featuresdescribed above, further aspects, embodiments, and features will becomeapparent by reference to the drawings and the following detaileddescription. Other aspects, features, and advantages of the devicesand/or processes and/or other subject matter described herein willbecome apparent in the teachings set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the drawings primarily are forillustrative purposes and are not intended to limit the scope of theinventive subject matter described herein. The drawings are notnecessarily to scale; in some instances, various aspects of theinventive subject matter disclosed herein may be shown exaggerated orenlarged in the drawings to facilitate an understanding of differentfeatures. In the drawings, like reference characters generally refer tolike features (e.g., functionally similar and/or structurally similarelements).

FIGS. 1a-1b provide partial-cutaway perspective views in schematic formof an illustrative (a) nuclear fuel assembly and (b) fuel element in oneexemplary embodiment.

FIGS. 2a and 2b-2f , respectively, provide a flow chart of a process ofmaking a composition and illustrative details of the process in oneexemplary embodiment.

FIGS. 3a-3c provide optical micrographs showing the differentmicrostructures of iron-based compositions that have undergone differentprocesses in one exemplary embodiment.

FIGS. 4a and 4b-4e , respectively, provide a flow chart of a process ofmaking a composition and illustrative details of the process in anotherexemplary embodiment.

FIGS. 5a and 5b , respectively, provide a flow chart of a process ofusing a composition and illustrative details of the process in oneexemplary embodiment.

FIGS. 6a and 6b show a process outline of the major process steps usedto fabricate plate and tube products of Heats CH and DH.

FIG. 7 illustrates a representative transmission electron microscope(TEM) image illustrating the depth effect on voids created byirradiation.

FIG. 8 shows the swelling results for the heats illustrating thedifference in void swelling performance of the composition embodimentsrelative to the archived ACO-3.

FIG. 9 shows a TEM collage of void microstructure in the four heatsafter irradiation at 480° C. to 188 dpa with 0.2 appm He/dpa, in whichthe voids appear as the black pockets.

FIG. 10 shows a TEM collage of void microstructure in the four heatsafter irradiation at 460° C. to 188 dpa with 0.015 appm He/dpa.

DETAILED DESCRIPTION

Introduction

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings, theuse of similar or the same symbols in different drawings typicallyindicates similar or identical items, unless context dictates otherwise.

The illustrative embodiments described in the detailed description,drawings, and claims are not meant to be limiting. Other embodiments maybe utilized, and other changes may be made, without departing from thespirit or scope of the subject matter presented here.

One skilled in the art will recognize that the herein describedcomponents (e.g., operations), devices, objects, and the discussionaccompanying them are used as examples for the sake of conceptualclarity and that various configuration modifications are contemplated.Consequently, as used herein, the specific exemplars set forth and theaccompanying discussion are intended to be representative of their moregeneral classes. In general, use of any specific exemplar is intended tobe representative of its class, and the non-inclusion of specificcomponents (e.g., operations), devices, and objects should not be takenas limiting.

The present application uses formal outline headings for clarity ofpresentation. However, it is to be understood that the outline headingsare for presentation purposes, and that different types of subjectmatter may be discussed throughout the application (e.g.,device(s)/structure(s) may be described under process(es)/operationsheading(s) and/or process(es)/operations may be discussed understructure(s)/process(es) headings; and/or descriptions of single topicsmay span two or more topic headings). Hence, the use of the formaloutline headings is not intended to be in any way limiting.

Overview

By way of overview, provided in one embodiment is a method of making acomposition, the method comprising: heat treating a material includingan iron-based composition at a first temperature under a first conditionin which at least some of the iron-based composition is transformed intoan austenite phase; cooling the material to a second temperature at acooling rate under a second condition in which at least some of theiron-based composition is transformed into a martensite phase; and heattreating the material at a third temperature under a third condition inwhich carbides are precipitated.

Provided in another embodiment is a method of making a composition, themethod comprising: subjecting a material to at least one of colddrawing, cold rolling, and pilgering; heat treating the materialincluding an iron-based composition at a first temperature under a firstcondition in which at least some of the iron-based composition istransformed into an austenite phase; cooling the material to a secondtemperature at a cooling rate under a second condition in which at leastsome of the iron-based composition is transformed into a martensitephase; and heat treating the material at a third temperature under athird condition, in which carbides are precipitated.

Provided in another embodiment is a composition comprising:(Fe)a(Cr)b(M)c; wherein a, b, and c are each a number greater than zerorepresenting a weight percentage; M is at least one transition metalelement; b is between 11 and 12; c is between about 0.25 and about 0.9;and balanced by a; and the composition further includes at least N atbetween about 0.01 wt % and about 0.04 wt %.

Provided in another embodiment is a composition, comprising:(Fe)a(Cr)b(Mo, Ni, Mn, W, V)c; wherein a, b, and c are each a numbergreater than zero representing a weight percentage; b is between 11 and12; c is between about 0.25 and about 0.9; and balanced by a; at leastsubstantially all of the composition has a martensite phase; and thecomposition includes N at between about 0.01 wt % and about 0.04 wt %.

Provided in another embodiment is a method of using a fuel assembly,comprising: generating power using a fuel assembly, a fuel element ofwhich includes a composition, which is represented by a chemicalformula: (Fe)a(Cr)b(M)c; wherein a, b, and c are each a number greaterthan zero representing a weight percentage; M is at least one transitionmetal element; b is between 11 and 12; c is between about 0.25 and about0.9; and balanced by a; and the composition further includes at least Nat between about 0.01 wt % and about 0.04 wt %.

Provided in another embodiment is a fuel element comprising a tubularcomposition made by a method comprising: heat treating a materialincluding an iron-based composition at a first temperature under a firstcondition in which at least some of the iron-based composition istransformed into an austenite phase; cooling the material to a secondtemperature at a cooling rate under a second condition in which at leastsome of the iron-based composition is transformed into a martensitephase; and heat treating the material at a third temperature under athird condition, in which carbides are precipitated. In one embodiment,in compositions where nitrogen is present, the precipitation of carbidesmay be accompanied by precipitation of nitrides and carbonitrides.

Fuel Assembly

FIG. 1a provides a partial illustration of a nuclear fuel assembly 10 inaccordance with one embodiment. The fuel assembly may be a fissilenuclear fuel assembly or a fertile nuclear fuel assembly. The assemblymay include fuel elements (or “fuel rods” or “fuel pins”) 11. FIG. 1bprovides a partial illustration of a fuel element 11 in accordance withone embodiment. As shown in this embodiment, the fuel element 11 mayinclude a cladding material 13, a fuel 14, and, in some instances, atleast one gap 15.

Fuel may be sealed within a cavity by the exterior cladding material 13.In some instances, the multiple fuel materials may be stacked axially asshown in FIG. 1b , but this need not be the case. For example, a fuelelement may contain only one fuel material. In one embodiment, gap(s) 15may be present between the fuel material and the cladding material,though gap(s) need not be present. In one embodiment, the gap is filledwith a pressurized atmosphere, such as a pressured helium atmosphere.

A fuel may contain any fissionable material. A fissionable material maycontain a metal and/or metal alloy. In one embodiment, the fuel may be ametal fuel. It can be appreciated that metal fuel may offer relativelyhigh heavy metal loadings and excellent neutron economy, which isdesirable for breed-and-burn process of a nuclear fission reactor.Depending on the application, fuel may include at least one elementchosen from U, Th, Am, Np, and Pu. The term “element” as represented bya chemical symbol herein may refer to one that is found in the PeriodicTable—this is not to be confused with the “element” of a “fuel element”.In one embodiment, the fuel may include at least about 90 wt % U—e.g.,at least 95 wt %, 98 wt %, 99 wt %, 99.5 wt %, 99.9 wt %, 99.99 wt %, orhigher of U. The fuel may further include a refractory material, whichmay include at least one element chosen from Nb, Mo, Ta, W, Re, Zr, V,Ti, Cr, Ru, Rh, Os, Ir, and Hf. In one embodiment, the fuel may includeadditional burnable poisons, such as boron, gadolinium, or indium.

The metal fuel may be alloyed with about 3 wt % to about 10 wt %zirconium to stabilize dimensionally the alloy during irradiation and toinhibit low-temperature eutectic and corrosion damage of the cladding. Asodium thermal bond fills the gap that exists between the alloy fuel andthe inner wall of the cladding tube to allow for fuel swelling and toprovide efficient heat transfer, which may keep the fuel temperatureslow. In one embodiment, individual fuel elements 11 may have a thin wire12 from about 0.8 mm diameter to about 1.6 mm diameter helically wrappedaround the circumference of the clad tubing to provide coolant space andmechanical separation of individual fuel elements 56 within the housingof the fuel assemblies 18 and 20 (that also serve as the coolant duct).In one embodiment, the cladding 13, and/or wire wrap 12 may befabricated from ferritic-martensitic steel because of its irradiationperformance as indicated by a body of empirical data.

Fuel Element

A “fuel element”, such as element 11 shown in FIGS. 1a-1b , in a fuelassembly of a power generating reactor may generally take the form of acylindrical rod. The fuel element may be a part of a power generatingreactor, which is a part of a nuclear power plant. Depending on theapplication, the fuel element may have any suitable dimensions withrespect to its length and diameter. The fuel element may include acladding layer 13 and a fuel 14 disposed interior to the cladding layer13. In the case of a nuclear reactor, the fuel may contain (or be) anuclear fuel. In one embodiment, the nuclear fuel may be an annularnuclear fuel. The fuel element may additionally include a liner disposedbetween the nuclear fuel 14 and the cladding layer 13. The liner maycontain multiple layers.

The fuel may have any geometry. In one embodiment, the fuel has anannular geometry. In such an embodiment, a fuel in an annular form mayallow a desirable level of fuel density to be achieved after a certainlevel of burn-up. Also, such an annular configuration may maintaincompressive forces between the fuel and the cladding to promote thermaltransport. The fuel may be tailored to have various properties,depending on the application. For example, the fuel may have any levelof density. In one embodiment, it is desirable to have a high density offuel, such as one as close to theoretical density uranium (in the caseof a fuel containing uranium) as possible. In another embodiment, havinga high porosity (low density) may prevent formation of additionalinternal voids during irradiation, decreasing fuel pressure onstructural material, such as cladding, during operation of the nuclearfuel.

The cladding material for the cladding layer 13 may include any suitablematerial, depending on the application. In one embodiment, the claddinglayer 13 may include at least one material chosen from a metal, a metalalloy, and a ceramic. In one embodiment, the cladding layer 13 maycontain a refractory material, such as a refractory metal including atleast one element chosen from Nb, Mo, Ta, W, Re, Zr, V, Ti, Cr, Ru, Rh,Os, Ir, Nd, and Hf. In another embodiment, the cladding material may bechosen from a ceramic material, such as silicon carbide or aluminumoxide (alumina).

A metal alloy in cladding layer 13 may be, in one exemplary embodiment,steel. The steel may be chosen from an austenitic steel, aferritic-martensitic steel, an oxide-dispersed steel, T91 steel, T92steel, HT9 steel, 316 steel, and 304 steel. The steel may have any typeof microstructure. For example, the steel may include at least one of amartensite phase, a ferrite phase, and an austenite phase. In oneembodiment, substantially all of the steel has at least one phase chosenfrom a martensite phase, a ferrite phase, and an austenite phase.Depending on the application, the microstructure may be tailored to havea particular phase (or phases). The cladding layer 13 may include aniron-based composition as described below.

At least some of the components of the fuel elements may be bonded. Thebonding may be physical (e.g., mechanical) or chemical. In oneembodiment, the nuclear fuel and the cladding are mechanically bonded.In one embodiment, the first layer and the second layer are mechanicallybonded.

Iron-Based Composition

Provided in one embodiment herein is a composition including a metal.The metal may include at least one of a metal, metal alloy, andintermetallic composition. In one embodiment, the metal includes iron.In one embodiment, the composition includes an iron-based composition.The term “X-based” composition in one embodiment may refer to acomposition including a significant amount an element X (e.g., metalelement). The amount may be, for example, at least 30%—e.g., at least40%, at least 50%, at least 60%, at least 70%, at least 80%, at least90%, at least 95%, at least 99%, or more. The percentage herein mayrefer to weight percent or a volume (or atomic) percent, depending onthe context. In one embodiment, the iron-based composition may includesteel.

The compositions described herein may be employed as a component of anuclear fuel element, such as the cladding material thereof. However,the metal-containing composition need not be limited to claddingmaterial and may be employed wherever such a composition is employed.For example, provided in one embodiment is a composition that isrepresented by the chemical formula (Fe)a(Cr)b(M)c, wherein a, b, and care each a number greater than zero representing a weight percentage;depending on the context, these numbers may alternatively represent avolume percentage. In one embodiment, b is a number between 11 and 12, cis between about 0.25 and about 0.9; balanced by a. In one embodiment,the composition includes at least nitrogen (“N”) at between about 0.005wt % and about 0.05 wt %—e.g., about 0.01 wt % and about 0.04 wt %,between about 0.01 wt % and about 0.03 wt %, between about 0.02 wt % andabout 0.03 wt %, etc. The element M may represent at least onetransition metal element. The element M in this iron-based compositionmay be any transition metal element found in the Periodic Table—e.g.,the elements in Groups 3-12 of the Periodic Table. In one embodiment, Mrepresents at least one of Mo, Ni, Mn, W, and V.

In another embodiment, the composition may include (or be) an iron-basedcomposition including a steel composition. The composition may berepresented by the chemical formula: (Fe)a(Cr)b(Mo, Ni, Mn, W, V)c,wherein a, b, and c are each a number greater than zero representing aweight percentage; depending on the context, the numbers mayalternatively represent a volume percentage. In one embodiment, thenumber b is between 11 and 12; c is between about 0.25 and about 0.9;balanced by a. In one embodiment, the composition includes N at betweenabout 0.01 wt % and about 0.04 wt %.

The composition may contain at least one additional element. Theadditional element may be a non-metal element. In one embodiment, thenon-metal element may be at least one element chosen from Si, S, C, andP. The additional element may be a metal element, including Cu, Cr, Mo,Mn, V, W, Ni, etc. In one embodiment, the composition further includesCr at between about 10 wt % and about 12.5 wt %; C at between about 0.17wt % and about 0.22 wt %; Mo at between about 0.80 wt % and about 1.2 wt%; Si less than or equal to about 0.5 wt %; Mn less than or equal toabout 1.0 wt %; V at between about 0.25 wt % and about 0.35 wt %; W atbetween about 0.40 wt % and about 0.60 wt %; P less than or equal toabout 0.03 wt %; and S less than or equal to about 0.3 wt %. In anotherembodiment, the composition further includes Ni at between about 0.3 wt% and 0.7 wt %. In another embodiment, the composition further includesCr at about 11.5 wt %; C at about 0.20 wt %; Mo at about 0.90 wt %; Niat about 0.55 wt %; Mn at about 0.65 wt %; V at about 0.30 wt %; W atabout 0.50 wt %; Si at about 0.20 wt % and N at about 0.02 wt %. Otherelements may also be present in any suitable amount. In some cases,certain incidental impurities may be present.

The composition may include an iron-based composition that includes asteel composition including a tailored microstructure. For example, thecompositions provided herein may have a small amount of a delta-ferritephase. In one embodiment, the composition is at least substantially freeof delta-ferrite. In another embodiment, the composition is completelyfree of delta-ferrite. Instead of a ferrite phase, the composition mayinclude a martensite phase (e.g., tempered martensite). In oneembodiment, substantially all of the composition has a martensite phase.In another embodiment, completely all of the composition has amartensite phase. As described below, one technique of tailoring themicrostructure (e.g., to mitigate formation of a ferrite phase) may beto control the content of nitrogen within the range provided herein.Mitigation herein may refer to reduction and/or prevention but need notrefer to total elimination.

The microstructure, including the phases, may be described in terms of achromium equivalent. In one embodiment, chromium equivalent (“Cr_(eq)”)is the sum of ferrite forming elements plotted in constitution diagramsfor the estimation of phases in stainless steel, weld metal, andcalculated from various equations. In some instances, chromiumequivalent may be used in conjunction with nickel equivalent, which isthe sum of austenite forming elements. The equation may be any suitableequation, depending at least on the material chemistry. In oneembodiment, the equation may be represented by the net chromiumequivalent, net Cr_(eq) which is the difference between chromiumequivalent and nickel equivalent. Net Cr_(eq) (wt %)=(% Cr)+6(% Si)+4(%Mo)+11(% V)+5(% Nb)+1.5(% W)+8(% Ti)+12(% Al)−4(% Ni)−2(% Co)−2(% Mn)−(%Cu)−40(% C)−30(% N). In one embodiment, the compositions describedherein may have Cr_(eq) of less than or equal to about 10—e.g., lessthan or equal to about 9, 8, 7, 6, 5, 4, 3, 2, or less. In oneembodiment, the Cr_(eq) may be kept under 9 to mitigate formation offerrites. Based on the equation above, N-content may play an importantrole in the value of Cr_(eq), and hence the ferrite formation (or lackthereof).

Due at least in part to the microstructure, the compositions describedherein may have tailored material properties. For example, thecompositions may have a high thermal stability. Thermal stability of acomposition in one embodiment may refer to the resistance of aparticular phase of the composition to decomposition (or dissociation)into another phase at an elevated temperature. In one embodiment, thecompositions described herein are substantially thermally stable at atemperature of greater or equal to about 500° C.—e.g., greater or equalto about 550° C., about 600° C., or higher.

The compositions provided herein may include additional phase(s) ormaterial(s). For example, in a case where the composition includescarbon, the carbon element may be present in the form of a carbide. Inone embodiment, the composition may include carbides distributedsubstantially uniformly in the composition. The carbides may have anysuitable sizes, depending on the application. In one embodiment, thecarbides have a size of less than or equal to about 2 microns—e.g., lessthan or equal to about 1 micron, 0.5 microns, 0.2 microns, 0.1 microns,or smaller.

Methods of Making/Using the Iron-Based Composition

The iron-based composition and a fuel element including the compositiondescribed herein may be manufactured by a variety of techniques. Theiron-based composition may be any of the compositions described herein.For example, the composition may include a steel. Provided in anotherembodiment is a fuel element having a tubular structure made by themethods described herein. For example, referring to FIG. 2a , providedin one embodiment is a method of making a composition; the methodincludes heat treating a material including an iron-based composition ata first temperature under a first condition in which at least some ofthe iron-based composition is transformed into an austenite phase (step201); cooling the material to a second temperature at a cooling rateunder a second condition in which at least some of the iron-basedcomposition is transformed into a martensite phase (step 202); and heattreating the material at a third temperature under a third condition inwhich carbides are precipitated (step 203). In one embodiment, steps 201and 202 together may be referred to as normalization, whereas step 203may be referred to as tempering.

The first temperature may be any temperature suitable for the firstcondition. In one example, the first temperature may be above theaustenitization temperature of the composition the temperature at whichsubstantially all of the ferrite phase of the iron-basedcomposition—transforms to an austenite phase. The austenite temperaturevaries with the material chemistry. In one embodiment, the firsttemperature is between about 900° C. and about 1200° C.—e.g., about1000° C. and about 1150° C., about 1025° C. and about 1100° C., etc. Thefirst temperature may be higher than 1200° C. or lower than 900° C.,depending on the material. In an embodiment, the processing of the steelcomposition includes transforming at least some of the steel compositioninto an austenite phase by heating the steel composition to atemperature from 1100° C. to 1300° C. for 40-60 hours.

Referring to FIG. 2b , the process of heat treating at the firsttemperature may further comprise heating the material to the firsttemperature (step 204). Heat treating at the first temperature may becarried out for any suitable length of time, depending on the materialinvolved. The time may be adjusted such that the length is sufficientlylong to promote formation of a homogeneous austenite solid solution. Inone embodiment, the heat treatment may be carried out for about at least3 minutes—e.g., at least 4 minutes, 5 minutes, 15 minutes, 20 minutes,30 minutes, 60 minutes, 90 minutes, 120 minutes, 150 minutes, 180minutes, or more. A longer or shorter length of time is also possible.In one embodiment, heat treating at the first temperature may be carriedout for between about 1 minute and about 200 minutes—e.g., about 2minutes and about 150 minutes, about 3 minutes and about 120 minutes,about 5 minutes and about 60 minutes, etc. In one embodiment, duringheat treating at the first temperature (e.g. at the end of thetreatment), at least some of the iron-based composition is transformedinto an austenite phase. In one embodiment, substantially all of thecomposition is transformed into an austenite phase. In anotherembodiment, completely all of the composition is transformed into anaustenite phase. In one embodiment, the first condition mitigatesformation of a delta-ferrite phase of the iron-based composition. Inanother embodiment, the first condition promotes transformation ofsubstantially all of the iron-based composition into an austenite phase.

Referring to FIG. 2c , the process of heat treating at the firsttemperature (step 201) may further comprise dissolving at leastsubstantially all of the carbides, if any, present in the iron-basedcomposition of the material (step 205).

The second temperature in step 202 may be any temperature suitable forthe second condition. In one embodiment, the second temperature is lessthan or equal to 60° C.—e.g., less than or equal to 50° C., 40° C., 30°C., 20° C., 10° C., or less. In one embodiment, the second temperatureis about room temperature (e.g., 20° C.). Cooling may be carried out viaany suitable techniques. In one embodiment, cooling includes cooling byat least one of air and liquid. In one embodiment, the second conditionpromotes transformation of substantially all of the iron-basedcomposition into a martensite phase. For example, the cooling may becarried out at a sufficient rate such that during cooling (e.g. at theend of the treatment), at least some of the iron-based composition istransformed into a martensite phase. In one embodiment, the rate is highenough that substantially all of the composition is transformed into amartensite phase. In another embodiment, the rate is high enough thatcompletely all of the composition is transformed into a martensitephase. In one embodiment, at the end of cooling the composition issubstantially free of at least one phase chosen from a ferrite phase andan austenite phase. In one embodiment, at the end of cooling thecomposition is completely free of at least one phase chosen from aferrite phase and an austenite phase.

The third temperature in step 203 may be any temperature suitable forthe third condition. The third temperatures may be lower than thetemperature above which austenite begins to form. In one embodiment, thethird temperature may be lower than the first temperature. In oneembodiment, the third temperature is at least 500° C.—e.g., at least550° C., 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., 900° C.,or more. In one embodiment, the third temperature is between about 500°C. and about 900° C.—e.g., about 550° C. and about 850° C., about 600°C. and about 800° C., about 650° C. and about 780° C., about 700° C. andabout 750° C., etc. A higher or lower temperature is also possible. Thethird temperature may be high enough to precipitate carbides and imparthigh temperature stability of carbides but low enough that carbidedensity is high and the carbide size is small with a homogeneousdistribution of carbides for void swelling resistance.

Referring to FIG. 2d , heat treating at the third temperature mayinclude heating the material to the third temperature (step 206). Heattreating at the third temperature may be carried out for any suitablelength of time, depending on the material involved. In one embodiment,heat treating at the third temperature may be carried out for betweenabout 0.1 hours and about 5 hours—e.g., between about 0.2 hours to about4 hours, about 0.5 hours to about 3 hours, about 1 hours and about 2hours, etc. A longer or shorter length of time is also possible. In oneembodiment, the third condition may mitigate the formation of a ferritephase and/or an austenite phase of the iron-based composition. In oneembodiment, the composition is substantially free of a ferrite phaseand/or an austenite phase. The heat treatment may be carried out by anysuitable techniques. In one embodiment, heat treating at the thirdtemperature is carried out in a vertical furnace.

Additional process(es) may be involved. For example, referring to FIG.2e , the method may further comprise cooling the composition from thethird temperature to a fourth temperature (step 207). The fourthtemperature may be lower than the third temperatures. For example, thefourth temperature may less than or equal to 60° C.—e.g., less than orequal to 50° C., 40° C., 30° C., 20° C., 10° C., or less. In oneembodiment, the fourth temperature is about room temperature (e.g., 20°C.). Referring to FIG. 2f , the method may further comprise controllingthe wt % of N in the iron-based composition of the material to mitigategrowth of a carbide phase of the iron-based composition (step 208).

Referring to FIGS. 3a-3c , the differences in microstructure of theiron-based composition are illustrated in the figures. FIG. 3a shows amicrostructure with blocky delta ferrite grains, loss of temperedmartensite microstructure, and many grains devoid of complex carbidemicrostructure, in conventional steel. FIG. 3b shows an improvedmicrostructure, with more homogenous carbide microstructure in thetempered martensite grains—note there are still some small delta ferritegrains in the microstructure. FIG. 3c shows a result of subjecting asteel sample to the processes described herein. The figure showsimproved microstructure substantially free of delta ferrite with mostgrain regions having a high density of finely distributed carbides.

Another embodiment provides an alternative method of making of acomposition. Referring to FIG. 4a , the method includes: subjecting amaterial to at least one of cold drawing, cold rolling, and pilgering(step 401); heat treating the material including an iron-basedcomposition at a first temperature under a first condition in which atleast some of the iron-based composition is transformed into anaustenite phase (step 402); cooling the material to a second temperatureat a cooling rate under a second condition in which at least some of theiron-based composition is transformed into a martensite phase (step403); and heat treating the material at a third temperature under athird condition, in which carbides are precipitated (step 404).

In step 401, the material is cold worked; cold drawing, cold rolling,and pilgering are only some examples of processes that the material maybe subjected to. One result of cold working is that the materialdimension may be changed to a desired value. For example, the thicknessof the material may be reduced as a result of cold working. In oneembodiment, the reduction in thickness may be, for example, by at least5%—e.g., at least 10%, 15%, 20%, 25%, or more. In one embodiment, thereduction is between about 5% and about 20%—e.g., between about 8% andabout 16%, between about 10% and about 15%, etc. Higher or lower valuesare also possible.

The dimension(s) of the material may be controlled via additionalprocesses. In one embodiment, the ingot may undergo a thermo-mechanicalprocessing to form the material with the final desired dimension(s).Referring to FIG. 4b , the starting material to be processed may be abillet, ingot, forging, etc., that has a cylindrical shape (step 405).The starting material is then mechanically worked (e.g., cold worked) bysuitable tube-manufacturing process(es) (step 406). When thetube-manufacturing process involves cold work, the work piece may beannealed (“intermediate annealing”) after the working process at atemperature below the temperature above which austenite begins toform—below a transformation temperature from ferrite phase to anaustenite phase (step 407). In one embodiment, austenite needs to beavoided because it would transform on cooling to hard martensite, thuscounteracting the softening process. Steps 406 and 407 are repeateduntil the final dimensions are achieved. In one embodiment, after thefinal cold working step (step 408) that provides the tube with its finaldimensions, the tube is not annealed again. The tube then may undergonormalization and tempering, as described above.

The method may include additional processes. Referring to FIG. 4c , themethod may further comprise extruding an ingot including the composition(step 409). Referring to FIG. 4d , the method may further compriseforming an ingot including the iron-based composition before thesubjecting step, wherein the forming includes at least one processchosen from cold cathode induction melting, vacuum induction melting,vacuum arc re-melting, and electro-slag remelting (step 410). Referringto FIG. 4e , the method may further comprise forming an ingot includingthe iron-based composition and purifying the ingot to remove impurities(e.g., P, S, etc.) before the subjecting step (step 411). The formingand the purifying processes may involve any suitable techniques. Theaforedescribed temperatures may vary depending on the materials and/orapplications thereof involved.

A fuel element (and fuel assemblies) including the composition (e.g., asthe cladding) may be used in a variety of applications. Provided in oneembodiment is a method of using a fuel assembly. Referring to FIG. 5a ,the method includes generating power using a fuel assembly, a fuelelement of which includes any of the iron-based compositions describedherein (step 501). Referring to FIG. 5b , the generation of power mayinclude generating at least one of electrical power and thermal power(step 502).

Power Generation

As described above, the fuel assemblies described herein may be a partof a power or energy generator, which may be a part of a powergenerating plant. The fuel assembly may be a nuclear fuel assembly. Inone embodiment, the fuel assembly may include a fuel, a plurality offuel elements, and a plurality of fuel ducts, such as those describedabove. The fuel ducts may include the plurality of fuel elementsdisposed therein.

The fuel assembly described herein may be adapted to produce a peakareal power density of at least about 50 MW/m²—e.g., at least about 60MW/m², about 70 MW/m², about 80 MW/m², about 90 MW/m², about 100 MW/m²,or higher. In some embodiments, the fuel assembly may be subjected toradiation damage at a level of at least about 120 displacements per atom(“DPA”)—e.g., at least about 150 DPA, about 160 DPA, about 180 DPA,about 200 DPA, or higher.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in any Application Data Sheet, are incorporated herein byreference in their entirety, to the extent not inconsistent herewith. Inthe event that one or more of the incorporated literature and similarmaterials differs from or contradicts this application, including butnot limited to defined terms, term usage, described techniques, or thelike, this application controls.

EXAMPLES

Embodiments of the composition described above were made and tested forvoid swelling performance. Three heats, identified as Heats FD, CH, andDH, of the composition were prepared to meet the specification listedabove. Heats CH and DH are the same composition that differ only in aslight variation in the final heat treatment. For relative comparisonbetween historic HT9 and the embodiments of the composition describedherein, a historical HT9 sample of heat 84425 from the ACO-3 duct usedin the Fast Flux Test Facility (FFTF) was tested for swelling using thesame protocol.

The actual composition of the final plate product of each heat wasdetermined by analysis and is shown in Table 1. The actual compositionof the historical sample was also determined and is likewise presentedin Table 1.

TABLE 1 Heats CH Historical HT9 Heat FD and DH ACO-3 Element Max. Min.Actual Actual Actual Fe Bal. Bal. Bal. Bal. Bal. C 0.19 0.17 0.176 0.200.20 Si 0.23 0.17 0.21 0.22 0.27 Mn 0.53 0.47 0.50 0.69 0.58 P 0.01 —<0.005 0.004 0.003 S 0.003 — 0.0017 0.001 0.004 Cr 12.2 11.8 12.12 11.5611.87 Mo 1.05 0.95 1.01 0.88 1.02 Ni 0.55 0.45 0.52 0.56 0.53 V 0.330.27 0.30 0.315 0.30 W 0.65 0.55 0.60 0.49 0.37 N 0.013 0.007 0.0110.023 0.0017 Cu 0.02 — <0.01 — 0.013 Al — — — — 0.002 Nb — — — <0.004<0.010 Co — — — — 0.011Heat FD Preparation

A 50 kg VIM ingot of Heat FD steel was heated at 1,200° C. for 48 hoursto homogenize the cast structure and then was forged to approximately 70t×100 w×450 L (mm). The temperature of furnace for homogenizing wascontrolled by PID temperature controller and by using calibratedthermocouple. The forged plate was soaked at 1,200° C. for 2 hours andhot-rolled from 70 t×100 w×450 L (mm) to approximately 24 t×110 w×1,050L (mm).

A portion of the hot-rolled steel plate was annealed at 800° C. for 1hour in order to make easy surface machining and approximately 0.3 mmper side was machined off the surface plate to remove any oxide film.The plate was then cold-rolled to a thickness of 5.4 mm by multiplesteps. At the intermediate passes during cold rolling, the plate wasannealed at 800° C. for 1 hour for softening cold-worked structure.Again, the furnace temperature for intermediate heat treatment iscontrolled by the PID temperature controller of furnace and by usingcalibrated thermocouple.

After cold rolling, the plate was annealed at 800° C. for 1 hour inorder to make easy sawing and was cut to smaller pieces for final heattreatment.

After cutting, final heat treatment was performed for on one of thesmaller pieces. This piece, designated Heat FD, was heat-treated (aspart of a batch of pieces of other steels) at 1,000° C. for 30 minutesand then air-cooled to room temperature in order to obtain martensitestructure. The temperature of furnace for normalization heat treatmentwas controlled by PID temperature controller and by using calibratedthermocouple. Furthermore, new thermocouples were attached by spotwelding on the surface of one of the pieces in the heat treatment batch.The batch including the piece attached to thermocouples was put in thefurnace at the normalization temperature, and final normalization heattreatment time started to count after thermocouples attached on piecereached the normalization temperature. After holding for prescribedtime, the batch was taken out of the furnace.

The normalized piece of Heat FD was heat-treated at 750° C. for 0.5 hourin order to temper the martensite structure, and then was air-cooled toroom temperature. The temperature of furnace for final temper heattreatment was controlled by PID temperature controller and by usingcalibrated thermocouple. Again, the Heat FD piece was part of a batch ofother steel pieces that included a piece with attached thermocouples asdescribed above. The batch was put in the furnace kept at the temperingtemperature, and final tempering treatment time started to count afterthermocouples attached on piece reached the tempering temperature or750° C. After holding for 30 minutes, the tempered batch was taken outof the furnace.

The Vickers hardness of the tempered Heat FD piece was tested threetimes and determined to be 238, 246, and 241 for an average of 242.

Heat CH and DH Preparation

FIGS. 6a and 6b show a process outline of the major process steps usedto fabricate plate and tube products of Heats CH and DH. The earlyprocessing steps (vacuum induction melting (VIM), vacuum arc re-melting(VAR) and homogenization were applied for both Heats.

One peculiarity of the fabrication process is the application of asecond homogenization heat treatment at 1180° C. for 48 hours, eitherafter hot rolling of the plate or after the 2^(nd) or 3^(rd) coldrolling step for the tube.

Swelling Testing

Heavy ion irradiation testing was conducted on plates of each of thethree heats and the historic control sample to determine the swellingperformance of the composition. Irradiations were conducted in an ionbeam laboratory using a dual ion (Fe⁺⁺ and He⁺⁺) irradiation beam tosimulate the production of He from (n,α) reactions and the subsequentformation of voids in a neutron environment. Energetic 5 MeV Fe⁺⁺ andlow current He⁺⁺ ions were directed at the steel samples at temperaturesof 440, 460, and 480° C. to an irradiation dose level of 188 dpa. ˜2 MeVHe⁺⁺ ions are transmitted through an Al foil with a thickness of ˜3 μmin order to degrade their energy and deposit the He⁺ at the appropriatedepth in the steel. The precise He⁺⁺ beam energy is dependent on theexact thickness of the Al foil. The Al foil is rotated relative to theHe⁺⁺ beam in order change the incidence angle of the beam and modify thedepth of implantation in the steel to range from 300-1000 nm. Theincidence angle varies from 0-60° at five different intervals, withdifferent hold times for each incidence angle, producing five separatedepth profiles that cumulatively provide a roughly uniform (±10%) Heconcentration from 300-1000 nm into the steel.

The irradiations were conducted on the three heats and the historicalcontrol sample using a 3 MV Pelletron accelerator. Samples wereirradiated using a combination of a defocused 5 MeV Fe⁺⁺ ion beam withtypical beam current of ˜100-400 nA on the samples and a 3 mm diameterfocused ˜2 MeV He⁺⁺ beam that was raster scanned at 0.255 kHz in x and1.055 kHz in y. Before each irradiation, the stage was outgassed to apressure below 1×10⁻⁷ torr. The beam current was recorded every 30-60minutes using the Faraday cup immediately in front of the samples andthe integrated charge (current×time) was converted to dose based on thedamage rate output of Stopping Range of Ions in Matter (SRIM)calculation at a depth of 600 nm using the Quick Kinchin-Pease mode anda 40 eV displacement energy.

The samples were mechanically polished using SiC paper up to a fine gritof #4000 followed by final polishing with diamond solutions up to 0.25μm, with a final mechanical polishing of 0.02 colloidal silica solutionprior to irradiation. After mechanical polishing, specimens wereelectropolished for 20 seconds in a 90% methanol and 10% perchloric acidsolution, at temperatures between −40° C. and −50° C., with an appliedpotential of 35 V between the specimen and platinum mesh cathode.

Temperature control was achieved by using a series of thermocouplesaffixed to irradiation samples that are heated and then used tocalibrate a two-dimensional imaging pyrometer at the irradiationtemperature. Temperature was controlled using the imaging pyrometer to±10° C. throughout the irradiation.

Irradiated sample preparation was accomplished using cross-sectionfocused ion beam (FIB) liftouts from the irradiated surface of eachsample. The liftout method allows the entire irradiation damage regionto be imaged, and for void imaging analysis to be consistently performedonly at the desired depth.

FIG. 7 illustrates a representative transmission electron microscope(TEM) image illustrating the depth effect on voids created byirradiation. Void imaging was done on a JEOL 2100F TEM. Voidmeasurements included only voids that were within a damage zone depth of300-700 nm into the sample, as represented by FIG. 7. By performing theanalysis in this way, all voids at the surface (0-300 nm), which wouldbe influenced by surface effects and changes in surface composition,were not taken into account. So, too, all voids at the end of damagecurve (>700 nm) that may be affected by self-interstitial implantationof the Fe⁺⁺ ion were not considered. Self-interstitial ions at the endof the damage curve tend to suppress void nucleation by affecting thevacancy/interstitial bias that causes void nucleation.

Sample thickness was measured using electron energy loss spectroscopy(EELS) to measure the zero energy loss fraction and determine samplethickness. Using sample thickness and image area, void density andswelling measurements can be made.

As mentioned above, the irradiations included a sample from the archivedACO-3 duct HT9 material from FFTF for a relative swelling comparison tothe composition embodiments described above. Heavy ion irradiations wereconducted on the four heats (CH, DH, FD, and ACO-3) described above inorder to generate a relative comparison in swelling behavior among thedifferent heats. The swelling response could also be compared to thearchive (heat 84425) of HT9 from ACO-3 duct wall from the FFTF program,irradiated at 443° C. to a dose of 155 dpa, which demonstrated swellingof ˜0.3% based on TEM imaging of the voids. Information regarding thehistoric heat of HT9 from FFTF program can be found in the article PhaseStability of an HT-9 Duct Irradiate in FFTF, by O. Anderoglu, et al.,Journal of Nuclear Materials 430 (2012) pp. 194-204.

To quantify the difference in swelling performance between theembodiments of the present compositions and the historic ACO-3 steel,the swelling % data in FIG. 8 were determined using process identifiedin Section 2.2 of the article Void Swelling And Microstructure EvolutionAt Very High Damage Level In Self-Ion Irradiated Ferritic-MartensiticSteels, by E. Getto, et al., Journal of Nuclear Materials 480 (2016) pp.159-176, which section is incorporated herein by reference. Whereverswelling % is used in this disclosure, it is calculated by the processidentified in the incorporated Section.

FIG. 8 shows the swelling results for the heats. FIG. 8 clearly showsthe difference in void swelling performance of the compositionembodiments relative to the archived ACO-3. At the lower and highertemperatures, 440° C. and 500° C., little swelling was detectable in anyof the heats. However, at temperatures of 460° C. and 480° C., each ofthe three heats of the present composition show significant improvementsin swelling over the historic ACO-3 steel.

FIG. 9 shows a TEM collage of void microstructure in the four heatsafter irradiation at 480° C. to 188 dpa with 0.2 appm He/dpa, in whichthe voids appear as the black features. The ACO-3 sample showed aninhomogeneous distribution of voids, but with a large cluster of manyvoids. The heats of the present composition each show a clearimprovement over the ACO-3. The differences between ACO-3 and the heatsof the present composition are striking and reflect a difference in voidincubation between ACO-3 and the embodiments of the steel compositionsdescribed herein.

FIG. 10 shows a TEM collage of void microstructure in the four heatsafter irradiation at 460° C. to 188 dpa with 0.015 appm He/dpa. Again,the heats of the present composition each show a clear improvement overthe ACO-3.

The examples provided above show that a steel of the composition:

Cr at between about 10.0 wt % and about 13.0 wt %;

C at between about 0.17 wt % and about 0.23 wt %;

Mo at between about 0.80 wt % and about 1.2 wt %;

Si less than or equal to about 0.5 wt %;

Mn less than or equal to about 1.0 wt %;

V at between about 0.25 wt % and about 0.35 wt %;

W at between about 0.40 wt % and about 0.60 wt %; and

Fe at least 80 wt %;

can be manufactured that exhibits a swelling of less than 0.9% byvolume, and in some cases less than 0.75%, less than 0.5%, and even lessthan 0.3% at a depth between 500-700 nm below the surface afterdual-beam Fe⁺⁺ and He⁺⁺ irradiation to doses of 188 displacements peratom (dpa) with 0.2 appm He/dpa, as calculated using the Stopping Rangein Matter simulation with the K-P option for damage cascades and a 40 eVdisplacement energy, created by irradiating the steel composition at460° C. with a defocused beam of 5 MeV Fe⁺⁺ ions and a raster-scannedbeam of ˜2 MeV He⁺⁺ ions transmitted through a thin Al foil forscattering and energy reduction to create a uniform He profile at theirradiation depth of the sample.

With respect to the use of substantially any plural and/or singularterms herein, those having skill in the art can translate from theplural to the singular and/or from the singular to the plural as isappropriate to the context and/or application. The varioussingular/plural permutations are not expressly set forth herein for sakeof clarity.

The herein described subject matter sometimes illustrates differentcomponents contained within, or connected with, different othercomponents. It is to be understood that such depicted architectures aremerely exemplary, and that in fact many other architectures may beimplemented which achieve the same functionality. In a conceptual sense,any arrangement of components to achieve the same functionality iseffectively “associated” such that the desired functionality isachieved. Hence, any two components herein combined to achieve aparticular functionality can be seen as “associated with” each othersuch that the desired functionality is achieved, irrespective ofarchitectures or intermedial components. Likewise, any two components soassociated can also be viewed as being “operably connected,” or“operably coupled,” to each other to achieve the desired functionality,and any two components capable of being so associated can also be viewedas being “operably couplable,” to each other to achieve the desiredfunctionality. Specific examples of operably couplable include, but arenot limited to, physically mateable and/or physically interactingcomponents, and/or wirelessly interactable, and/or wirelesslyinteracting components, and/or logically interacting, and/or logicallyinteractable components.

In some instances, one or more components may be referred to herein as“configured to,” “configured by,” “configurable to,” “operable/operativeto,” “adapted/adaptable,” “able to,” “conformable/conformed to,” etc.Those skilled in the art will recognize that such terms (e.g.“configured to”) can generally encompass active-state components and/orinactive-state components and/or standby-state components, unlesscontext requires otherwise.

While particular aspects of the present subject matter described hereinhave been shown and described, it will be apparent to those skilled inthe art that, based upon the teachings herein, changes and modificationsmay be made without departing from the subject matter described hereinand its broader aspects and, therefore, the appended claims are toencompass within their scope all such changes and modifications as arewithin the true spirit and scope of the subject matter described herein.It will be understood by those within the art that, in general, termsused herein, and especially in the appended claims (e.g., bodies of theappended claims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to claims containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that typically a disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms unless context dictates otherwise. For example, the phrase “Aor B” will be typically understood to include the possibilities of “A”or “B” or “A and B.”

With respect to the appended claims, those skilled in the art willappreciate that recited operations therein may generally be performed inany order. Also, although various operational flows are presented in asequence(s), it should be understood that the various operations may beperformed in other orders than those which are illustrated, or may beperformed concurrently. Examples of such alternate orderings may includeoverlapping, interleaved, interrupted, reordered, incremental,preparatory, supplemental, simultaneous, reverse, or other variantorderings, unless context dictates otherwise. Furthermore, terms like“responsive to,” “related to,” or other past-tense adjectives aregenerally not intended to exclude such variants, unless context dictatesotherwise.

Those skilled in the art will appreciate that the foregoing specificexemplary processes and/or devices and/or technologies arerepresentative of more general processes and/or devices and/ortechnologies taught elsewhere herein, such as in the claims filedherewith and/or elsewhere in the present application.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

Any portion of the processes described herein may be automated. Theautomation may be accomplished by involving at least one computer. Theautomation may be executed by program that is stored in at least onenon-transitory computer readable medium. The medium may be, for example,a CD, DVD, USB, hard drive, etc. The selection and/or design of the fuelelement structure, including the assembly, may also be optimized byusing the computer and/or a software program.

The above-described embodiments of the invention can be implemented inany of numerous ways. For example, some embodiments may be implementedusing hardware, software or a combination thereof. When any aspect of anembodiment is implemented at least in part in software, the softwarecode can be executed on any suitable processor or collection ofprocessors, whether provided in a single computer or distributed amongmultiple computers.

Also, the technology described herein may be embodied as a method, ofwhich at least one example has been provided. The acts performed as partof the method may be ordered in any suitable way. Accordingly,embodiments may be constructed in which acts are performed in any orderdifferent from that illustrated, which may include performing some actssimultaneously, even though shown as sequential acts in illustrativeembodiments.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “including” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of,” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

Any ranges cited herein are inclusive. The terms “substantially” and“about” used throughout this Specification are used to describe andaccount for small fluctuations. For example, they can refer to less thanor equal to ±5%, such as less than or equal to ±2%, such as less than orequal to ±1%, such as less than or equal to ±0.5%, such as less than orequal to ±0.2%, such as less than or equal to ±0.1%, such as less thanor equal to ±0.05%.

In the claims, as well as in the specification above, all transitionalphrases such as “including,” “carrying,” “having,” “containing,”“involving,” “holding,” “composed of,” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

The claims should not be read as limited to the described order orelements unless stated to that effect. It should be understood thatvarious changes in form and detail may be made by one of ordinary skillin the art without departing from the spirit and scope of the appendedclaims. All embodiments that come within the spirit and scope of thefollowing claims and equivalents thereto are claimed.

What is claimed is:
 1. A steel composition comprising: Cr at betweenabout 10.0 wt % and about 13.0 wt %; C at between about 0.17 wt % andabout 0.23 wt %; Mo at between about 0.80 wt % and about 1.2 wt %; Siless than or equal to about 0.5 wt %; Mn less than or equal to about 1.0wt %; V at between about 0.25 wt % and about 0.35 wt %; W at betweenabout 0.40 wt % and about 0.60 wt %; and Fe at least 80 wt %; whereinthe steel composition has been processed so that it exhibits a swellingof less than 0.9% by volume at a depth between 500-700 nm below thesurface after dual-beam Fe++ and He++ irradiation to doses of 188displacements per atom (dpa) with 0.2 appm He/dpa, as calculated usingthe Stopping Range in Matter simulation with the K-P option for damagecascades and a 40 eV displacement energy, created by irradiating thesteel composition at 460° C. with a defocused beam of 5 MeV Fe++ ionsand a raster-scanned beam of ˜2 MeV He++ ions transmitted through a thinAl foil for scattering and energy reduction to create a uniform Heprofile at the irradiation depth of a sample of the steel composition;wherein the processing of the steel composition includes transforming atleast some of the steel composition into an austenite phase by heatingthe steel composition to a temperature from 1100° C. to 1300° C. for40-60 hours.
 2. The steel composition of claim 1, wherein the steelcomposition exhibits a swelling of less than 0.75% by volume.
 3. Thesteel composition of claim 1, wherein the steel composition exhibits aswelling of less than 0.5% by volume.
 4. The steel composition of claim1, wherein the steel composition exhibits a swelling of less than 0.3%by volume.
 5. The steel composition of claim 1, wherein the steelcomposition is an HT9 steel.
 6. A fuel element made of the steelcomposition of claim
 1. 7. A component of a fuel assembly made of thesteel composition of claim
 1. 8. A steel composition comprising:(Fe)_(a)(Cr)_(b)(Mo, Ni, Mn, W, V)_(c)N_(d); wherein a, b, c, and d areeach a number greater than zero representing a weight percentage; b isbetween 11 and 13; c is between about 0.25 and about 0.9; d is betweenabout 0.01 and about 0.04; and balanced by a; and wherein the steelcomposition has been processed so that it exhibits a swelling of lessthan 0.9% by volume at a depth between 500-700 nm below the surfaceafter dual-beam Fe++ and He++ irradiation to doses of 188 displacementsper atom (dpa) with 0.2 appm He/dpa, as calculated using the StoppingRange in Matter simulation with the K-P option for damage cascades and a40 eV displacement energy, created by irradiating the steel compositionat 460° C. with a defocused beam of 5 MeV Fe++ ions and a raster-scannedbeam of ˜2 MeV He++ ions transmitted through a thin Al foil forscattering and energy reduction to create a uniform He profile at theirradiation depth of a sample of the steel composition; wherein theprocessing of the steel composition includes transforming at least someof the steel composition into an austenite phase by heating the steelcomposition to a temperature from 1100° C. to 1300° C. for 40-60 hours.9. The steel composition of claim 8, wherein b is between 11.5 and 12.5.10. The steel composition of claim 8, wherein the steel compositionexhibits a swelling of less than 0.75% by volume.
 11. The steelcomposition of claim 8, wherein the steel composition exhibits aswelling of less than 0.5% by volume.
 12. The steel composition of claim8, wherein the steel composition exhibits a swelling of less than 0.3%by volume.
 13. The steel composition of claim 8, wherein the steelcomposition is an HT9 steel.
 14. A fuel element made of the steelcomposition of claim
 8. 15. A component of a fuel assembly made of thesteel composition of claim 8.